1. Field of the Invention
This invention relates to a control system for use in an exhaust gas recirculation system of an internal combustion engine, in which part of exhaust gases from the engine is recirculated to an intake system to reduce the amount of harmful components contained in exhaust gases, and more particularly to a control system which controls the exhaust gas recirculation system so as to prevent lowering in the running performance of the engine due to the aforesaid exhaust gas recirculation.
2. Description of the Prior Art
It is known in the prior art that a part of exhaust gases may be returned to an intake system to dilute a mixture charge with inert gases for the purpose of lowering the combustion temperature, thereby reducing the amount of harmful components contained in exhaust gases, particularly nitrogen oxides (NOx). However, such an attempt poses the problem of lowering the running performance of an internal combustion engine. To avoid this shortcoming, an attempt has been proposed, in which ignition timing is controlled, coupled with the control of exhaust gas recirculation, in an attempt to compensate for the lowered running performance of an engine. The compensation for lowered running performance by an ignition timing control is indeed effective at a relatively high level of the nitrogen oxides, but difficult to attain at such a low level of the nitrogen oxide as required in current clean air legislation.